The long-term objective of this proposal is to elucidate the molecular mechanisms involved in actin ring formation and bone resorption. Bone resorption is the first step in bone remodeling. Actin ring formation has been shown to be a prerequisite for efficient bone resorption in osteoclasts. Recent preliminary studies from our laboratory suggest that N-WASP-Arp2/3 complex may have a role in the osteoclast actin ring formation. Tyrosine kinases such as PYK2 and Src are involved in the phosphorylation of N-WASP and N-WASP associated phosphoproteins. Moreover, tyrosine phosphatase (PTP-PEST) has a unique role in the modulation of tyrosine phosphorylation of N-WASP and the associated signaling molecules. We therefore hypothesize: 1. N-WASP coordinately activated by Cdc42, PtdIns P2 (PIP2), and kinase(s) can stimulate Arp2/3 mediated actin polymerization and actin ring formation in osteoclasts. 2. Src/PTP-PEST regulation of tyrosine phosphorylation of N-WASP and the associated signaling proteins is required for actin remodeling in the actin ring and bone resorption. Thus, our Specific Aims are to: 1. Determine the signal transduction mechanisms involved in N-WASP activation and actin ring formation. 2. Determine the regulation of tyrosine phosphorylation, actin ring formation, and bone resorption by PTP-PEST. The goal of this revised renewal application is to identify the underlying molecular mechanisms in actin ring formation. To advance the understanding of the mechanisms of bone resorption at the cellular and molecular level, different approaches will be used. HIV-TAT or adenoviral-mediated delivery of N-WASP, PTP-PEST, and kinases (Src and PYK2) into osteoclasts will be performed to identify the signal transduction mechanisms involved in the formation of N-WASP-Arp2/3 complex and actin ring. The binding sites of PTP-PEST with N-WASP will be characterized by the delivery of TAT-fused oligopeptides derived from proline-rich regions of PTP-PEST and N-WASP. We will analyze the effects of the above-mentioned treatments on actin ring formation and bone resorption. Identification of peptides that impede osteoclast function will be useful in the development of pharmacological agents, targeting osteoclast actin ring formation and bone resorption in disorders such as osteoporosis, periodontal disease, and osteoarthritis.